Impact of degenerate n-doping on the optical absorption edge in transparent conducting cadmium oxide

Impact of degenerate n-doping on the optical absorption edge in transparent conducting cadmium oxid

Sulfur passivation of surface electrons in highly Mg-doped InN

Electron accumulation with a sheet density greater than 1013 cm-2 usually occurs at InN surfaces. Here, the effects of treatment with ammonium sulfide ((NH 4)2 S x) on the surface electronic properties of highly Mg-doped InN (> 4 × 10 18 cm - 3) have been investigated with high resolution x-ray photoemission spectroscopy. The valence band photoemission spectra show that the surface Fermi level decreases by approximately 0.08 eV with (NH 4) 2 S x treatment, resulting in a decrease of the downward band bending and up to a 70% reduction in the surface electron sheet density. © 2013 AIP Publishing LLC

Surface structure of GaP(110): Ion scattering and density functional theory study

The structure of the GaP(110) surface has been investigated using coaxial impact collision ion scattering spectroscopy (CAICISS) and density functional theory (DFT). CAICISS simulations based on structural parameter values of the well known buckled dimer model obtained in quantitative low energy electron diffraction studies in the 1980s were found to fit well with experimental data measured in the [1̄10] azimuth, but offered a relatively poor fit in all other incident geometries. A new surface structure derived from DFT calculations, involving small changes to bond angles and interlayer spacings, was optimized during the analysis of CAICISS data, until good fits of the data were obtained for all three azimuths ([1̄10], [001], and [1̄11]). The key feature of the new structure found to be required for this improved agreement with experiment is the inclusion of relaxations both parallel and perpendicular to the surface between the second and third layers. © 2012 American Physical Society

Temperature dependence of the direct bandgap and transport properties of CdO

Temperature-dependent optical absorption, Hall effect, and infrared reflectance measurements have been performed on as-grown and post-growth annealed CdO films grown by metal organic vapor phase epitaxy on sapphire substrates. The evolution of the absorption edge and conduction electron plasmon energy with temperature has been modeled, including the effects arising from the Burstein-Moss shift and bandgap renormalization. The zero-temperature fundamental direct bandgap and band edge effective mass have been determined to be 2.31 ± 0.02 eV and 0.27 ± 0.01 m 0, respectively. The associated Varshni parameters for the temperature dependence of the bandgap are found to be α = 8 × 10-4 eV / K and β = 260 K. © 2013 American Institute of Physics

Liquid metals: An ideal platform for the synthesis of two-dimensional materials

The surfaces of liquid metals can serve as a platform to synthesise two-dimensional materials. By exploiting the self-limiting Cabrera-Mott oxidation reaction that takes place at the surface of liquid metals exposed to ambient air, an ultrathin oxide layer can be synthesised and isolated. Several synthesis approaches based on this phenomenon have been developed in recent years, resulting in a diverse family of functional 2D materials that covers a significant fraction of the periodic table. These straightforward and inherently scalable techniques may enable the fabrication of novel devices and thus harbour significant application potential. This review provides a brief introduction to liquid metals and their alloys, followed by detailed guidance on each developed synthesis technique, post-growth processing methods, integration processes, as well as potential applications of the developed materials

Influence of nonmagnetic Zn substitution on the lattice and magnetoelectric dynamical properties of the multiferroic material CuO

Dynamic magnetoelectric coupling in the improper ferroelectric Cu1-xZnxO (x=0,x=0.05) was investigated using terahertz time-domain spectroscopy to probe electromagnon and magnon modes. Zinc substitution was found to reduce the antiferromagnetic ordering temperature and widen the multiferroic phase, under the dual influences of spin dilution and a reduction in unit-cell volume. The impact of Zn substitution on lattice dynamics was elucidated by Raman and Fourier-transform spectroscopy, and shell-model calculations. Pronounced softenings of the Au phonons, active along the direction of ferroelectric polarization, occur in the multiferroic state of Cu1-xZnxO, and indicate strong spin-phonon coupling. The commensurate antiferromagnetic phase also exhibits spin-phonon coupling, as evidenced by a Raman-active zone-folded acoustic phonon, and spin dilution reduces the spin-phonon coupling coefficient. While the phonon and magnon modes broaden and shift as a result of alloy-induced disorder, the electromagnon is relatively insensitive to Zn substitution, increasing in energy without widening. The results demonstrate that electromagnons and dynamic magnetoelectric coupling can be maintained even in disordered spin systems. © 2014 American Physical Society

Nanostructured Electrodes Based on Two-Dimensional SnO2for Photoelectrochemical Water Splitting

Here we demonstrate the fabrication of two-dimensional SnO2nanosheet arrays and their use as electrodes for solar water oxidation. These nanosheets deposited on commercial transparent electrodes are used as substrates for the deposition of photoactive semiconductors including BiVO4and Fe2O3. These composite photoanodes show a marked enhancement in their photoelectrochemical (PEC) performance, including improved light absorption, lower onset potentials, and higher photocurrents. Importantly, SnO2nanosheets alone have negligible PEC activity, suggesting that their role is purely morphological (enhanced surface area) and electronic (surface passivation, improved charge extraction). Our results provide the foundation for further work on photoanode architectures for efficient water splitting

Surface electronic properties of In-rich InGaN alloys grown by MOCVD

The band bending, position of Fermi level at the cleaned surfaces and bulk Fermi level of In-rich InxGa1-xN alloys grown by metal-organic chemical vapor deposition with a composition of 0.20 ≤ x ≤ 1.00 have been investigated using X-ray photoemission spectroscopy, infrared reflectivity and Hall effect measurements. Wet etching of InxGa1-xN alloys in HCl successfully reduced the native oxides at the surface, allowing these measurements to be performed more accurately. Electron accumulation layers, accompanied by downward band bending, are present at the surface, with a decrease to flatband conditions occurring at x ≈ 0.2 with increasing Ga fraction. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic photovoltaic cells utilising ZnO electron extraction layers produced through thermal conversion of ZnSe

In this work, a thin ZnSe layer was deposited in a vacuum and then thermally annealed in air to provide an efficient electron extraction layer for an inverted organic photovoltaic (OPV) cell. Annealing the ZnSe film at 450 °C (ZnSe(450 °C)) increased the device performance and gave an efficiency of 2.83%. X-ray photoelectron spectroscopy (XPS) measurements show that the increased device performance upon annealing at 450 °C is due to the thermal conversion of ZnSe to ZnO. ZnO has a wider band gap than ZnSe, which allows for more light to reach the photoactive layer. The electronic structures of the treated ZnSe films were explored by ultraviolet photoemission spectroscopy (UPS) which showed that the ZnSe(450 °C) films had a Fermi level close to the conduction band edge, allowing for efficient electron extraction compared to the energetic barrier for extraction formed at the ZnSe(RT)/organic interface

Highly Conductive and Visibly Transparent p-Type CuCrO2 Films by Ultrasonic Spray Pyrolysis

The development of high-performing p-type transparent conducting oxides will enable immense progress in the fabrication of optoelectronic devices including invisible electronics and all-oxide power electronics. While n-type transparent electrodes have already reached widespread industrial production, the lack of p-type counterparts with comparable transparency and conductivity has created a bottleneck for the development of next-generation optoelectronic devices. In this work, we present the fabrication of delafossite copper chromium oxide p-type transparent electrodes with outstanding optical and electrical properties. These layers were deposited using ultrasonic spray pyrolysis, a wet chemical method that is fast, simple, and scalable. Through careful screening of the deposition conditions, highly crystalline, dense, and smooth CuCrO2 coatings were obtained. A detailed investigation of the role played by the deposition temperature and the cation ratio enabled the properties of the prepared layers to be reliably tuned, as verified using X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, Hall effect measurements, and electron and atomic force microscopies. We demonstrate record conductivities for solution-processed CuCrO2, exceeding 100 S cm-1, and we also obtained the highest value for two separate figures of merit for p-type transparent conducting oxides. These performances position solution-deposited CuCrO2 as the leading p-type transparent-conducting oxide currently available